Field of the Invention
The present disclosure relates generally to transistor device driver circuits, and more specifically to a segmented driver that segments driver operation for turning off a transistor device.
Description of the Related Art
High power switching functions (high voltage and/or high current) are used in a variety of applications, such as solar power, uninterruptible power supplies (UPS), motor control, electric vehicles (EV), hybrid EVs (HEV), etc. In the emerging EV/HEV market, for example, inverter circuits are often used to switch a DC input voltage across the phases of a three-phase motor. In most applications, efficiency is paramount in which it is desired to conserve as much energy as possible. In EV/HEV applications, for example, energy efficiency translates to fuel economy and electric range. The inversion process involves high power switching using high voltage electronic transistor switches. An insulated-gate bipolar transistor (IGBT) is particularly advantageous to implement each electronic switch in that it combines high efficiency with fast switching.
In many applications, the switching or inverting function is used to switch large currents between different branches of a high voltage system. Parasitic inductances in the system generate overshoot voltages that may be added to the source voltage during switching. Although it may be desired to switch as quickly as possible, the generated overshoot voltages cause excessive voltages that jeopardize system components including the electronic switches. The excessive voltages may damage or even catastrophically destroy the transistor device and other system components. In order to avoid this undesirable outcome, the voltage rating of the transistor devices may be increased. Alternatively, one or more passive devices may be placed between the control terminal of the transistor switching device and the driver circuit to slow down the switching process to reduce excessive voltage overshoot. For example, a resistor may be inserted between the driver (e.g., gate driver) and the control terminal (e.g., gate) of the transistor device (e.g., IGBT) to slow down switching to reduce voltage overshoot.
Transistor devices with higher voltage ratings may be available, but usually at significantly higher cost. On the other hand, resistors or the like inserted in the control path consume valuable energy during each switching cycle which significantly reduces efficiency. In this manner, a tradeoff often had to be made between selecting transistor devices with higher voltage ratings or adding circuitry that slowed down the switching process.